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Additional N (additional + n)

Distribution by Scientific Domains
Chemistry75%

Selected Abstracts

The response of heterotrophic activity and carbon cycling to nitrogen additions and warming in two tropical soils

GLOBAL CHANGE BIOLOGY, Issue 9 2010
DANIELA F. CUSACK
Abstract Nitrogen (N) deposition is projected to increase significantly in tropical regions in the coming decades, where changes in climate are also expected. Additional N and warming each have the potential to alter soil carbon (C) storage via changes in microbial activity and decomposition, but little is known about the combined effects of these global change factors in tropical ecosystems. In this study, we used controlled laboratory incubations of soils from a long-term N fertilization experiment to explore the sensitivity of soil C to increased N in two N-rich tropical forests. We found that fertilization corresponded to significant increases in bulk soil C concentrations, and decreases in C loss via heterotrophic respiration (P< 0.05). The increase in soil C was not uniform among C pools, however. The active soil C pool decomposed faster with fertilization, while slowly cycling C pools had longer turnover times. These changes in soil C cycling with N additions corresponded to the responses of two groups of microbial extracellular enzymes. Smaller active C pools corresponded to increased hydrolytic enzyme activities; longer turnover times of the slowly cycling C pool corresponded to reduced activity of oxidative enzymes, which degrade more complex C compounds, in fertilized soils. Warming increased soil respiration overall, and N fertilization significantly increased the temperature sensitivity of slowly cycling C pools in both forests. In the lower elevation forest, respired CO2 from fertilized cores had significantly higher ,14C values than control soils, indicating losses of relatively older soil C. These results indicate that soil C storage is sensitive to both N deposition and warming in N-rich tropical soils, with interacting effects of these two global change factors. N deposition has the potential to increase total soil C stocks in tropical forests, but the long-term stability of this added C will likely depend on future changes in temperature. [source]

Two 18, TiIV,5 -Cp-tris(sec -amido)-type complexes derived from 1H -imidazol-2-yl side-chain functionalized cyclopentadienes

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2009
Xiaowu Wang
Achiral {2-[2-(,5 -cyclopentadienyl)-2-methylpropyl]-1H -imidazolyl-,N1}bis(N,N -diethylamido-,N)titanium(IV), [Ti(C4H10N)2(C12H14N2)], (I), and closely related racemic (SR)-{2-[(,5 -cyclopentadienyl)(phenyl)methyl]-1H -imidazolyl-,N1}bis(N,N -diethylamido-,N)titanium(IV), [Ti(C4H10N)2(C15H12N2)], (II), have been prepared by direct reactions of Ti(NEt2)4 and the corresponding 1H -imidazol-2-yl side-chain functionalized cyclopentadienes. In compound (II), there are two crystallographically independent molecules of very similar geometries connected by a noncrystallographic pseudosymmetry operation akin to a 21 screw axis. All Ti-ligating N atoms in both (I) and (II) are in planar environments, which is indicative of an additional N,Ti p,,d, donation. This fact and the 18, nature of both (I) and (II) are additionally supported by quantum chemical single-point density functional theory (DFT) computations. [source]

Ethyl 2-amino-4- tert -butyl-1,3-thiazole-5-carboxyl­ate and 6-methylimidazo­[2,1- b]­thia­zole,2-amino-1,3-thia­zole (1/1)

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2004
Daniel E. Lynch
The structure of ethyl 2-amino-4- tert -butyl-1,3-thia­zole-5-carboxyl­ate, C10H16N2O2S, (I), and the structure of the 1:1 adduct 6-methyl­imidazo­[2,1- b]­thia­zole,2-amino-1,3-thia­zole (1/1), C6H6N2S·C3H4N2S, (II), have been determined. The mol­ecules in (I) associate via a hydrogen-bonded R(8) dimer consisting of N,H,N interactions, with the hydrogen-bonding array additionally involving N,H,O interactions to one of the carboxyl­ate O atoms. The 2-amino­thia­zole mol­ecules in (II) also associate via an N,H,N hydrogen-bonded R(8) dimer, with an additional N,H,N interaction to the Nsp2 atom of the imidazo­thia­zole moiety, creating hydrogen-bonded quartets. [source]

13C/12C Ratios of endogenous urinary steroids investigated for doping control purposes

DRUG TESTING AND ANALYSIS, Issue 2 2009
Thomas Piper
Abstract In order to detect the misuse of endogenous anabolic steroids such as testosterone by athletes a total of n = 1734 suspicious urine samples were investigated by gas chromatography/combustion/isotope ratio mass spectrometry throughout the years 2005, 2006 and 2007. The 13C/12C ratio of a target substance (androsterone, a testosterone metabolite) was compared to the 13C/12C ratio of an endogenous reference compound (11,-hydroxyandrosterone). N = 1340 samples were investigated due to elevated testosterone/epitestosterone ratios, with n = 87 (6.5%) exceptional findings regarding their isotopic ratios. An additional n = 164 samples were investigated because of elevated dehydroepiandrosterone concentrations, with n = 2 (1.2%) exceptional findings. The remainder were subjected to isotope ratio analysis because of elevated androsterone levels or because this was requested by sports federations. Significant differences between female and male samples were found for the 13C/12C ratios of androsterone and 11,-hydroxyandrosterone but not for samples taken in or out of competition. A further n = 645 samples originating from other World Anti-Doping Agency accredited laboratories, mainly throughout Europe as well as South America, South Africa and Southeast Asia, were investigated. The 13C/12C ratios of the urinary steroids differ significantly for each geographical region, reflecting the dietary status of the individuals. The system stability over time has been tested by repeated injections of a standard solution and repeated processing of frozen stored blank urine. Despite a drift over time in absolute 13C/12C ratios, no significant change in the difference of 13C/12C (11,-hydroxyandrosterone) minus 13C/12C (androsterone) could be observed. Copyright © 2009 John Wiley & Sons, Ltd. Copyright © 2009 John Wiley & Sons, Ltd. [source]